The present invention relates, in general, to display devices, and more particularly, to electro-luminescent displays and circuits.
Electro-luminescent displays are well known in the art and are used for a variety of display applications. FIG. 1 schematically illustrates a prior art circuit utilized for controlling thin film electro-luminescent displays. Such thin film electro-luminescent displays utilize a voltage divide capacitor (C.sub.1) and an open drain transistor (Q.sub.1) to control each pixel element of the display. An individual pixel of the electro-luminescent display functions as a capacitor C.sub.el. As illustrated by the connection of V.sub.ac to capacitor C.sub.el, an alternating voltage (V.sub.ac) is applied to one electrode of the pixel. Voltage V.sub.ac has a value that is greater than a threshold voltage of the pixel in order to ensure that the pixel emits light. As used herein, "threshold voltage" of the pixel means a voltage at which light generation is observed by an unaided human eye, and is also the voltage at which the onset of cyclic avalanche breakdown occurs within the pixel. Display information is provided as a DATA signal that is applied to Q.sub.1. When the DATA signal applied to Q.sub.1 is low, Q.sub.1 is disabled so that voltage V.sub.ac is divided between capacitors C.sub.1 and C.sub.el and no light is emitted by the pixel. When the DATA signal enables Q.sub.1, capacitor C.sub.1 is shorted and all of voltage V.sub.ac is across C.sub.el so that the pixel emits light.
One problem with the prior art circuits is that divider capacitor C.sub.1 is very large thereby limiting the number of pixels on the display. The combined area of Q.sub.1 and C.sub.1 is usually larger than the size of the pixel. Such a large size results in high display costs. Additionally, divider capacitors generally are built using thin silicon dioxide layers that result in low yields thereby further increasing display costs.
Accordingly, it is desirable to have an electro-luminescent display having a control circuit that occupies an area smaller than the pixel area, and that does not require a divider capacitor.